In spite of the advancement of technology, electronic devices are still restricted by power cables during charging process, which reduces the convenience of utility. Therefore, technology of the wireless charging is gradually paid attention in expectation of overcoming the defeat of the conventional charging method for electronic devices relying on tangible power cables to transfer energy.
Conventional technology of the wireless charging can be classified into magnetic induction, magnetic resonance, or electromagnetic wave transportation. After omitting the using of power cables, conductive contacts of the electronic devices can be hidden in the electronic devices without being exposing to outside.
Wireless charging by magnetic induction is the most often used wireless charging method. However, as charging by magnetic induction, electronic devices need to contact and be close to charging devices so as to form an induced magnetic field to transfer energy.
Comparing to wireless charging by magnetic induction, wireless charging by magnetic resonance has a longer charging distance. Electronic devices and charging devices can reach a specific resonance frequency by changing the frequency of magnetic field to transfer energy. However, efficiency of wireless charging by magnetic resonance is low and wireless charging by magnetic resonance still has risk to human body.
Comparing to wireless charging by magnetic induction or magnetic resonance, wireless charging by electromagnetic wave transportation has a further longer charging distance. In addition, method of wireless charging by electromagnetic wave transportation can charge many rechargeable batteries at the same time.
Nevertheless, energy provided by electromagnetic wave harvested in environment is low and the internal resistance of the rechargeable battery consumes portion of energy. As a result, the conventional rechargeable batteries still cannot efficiently utilize the electromagnetic wave as an energy source for wireless charging.